1. Field of the Invention
This invention relates to a process for producing a printed wiring board utilizing an electrophotographic method, particularly to a process for producing a printed wiring board utilizing a wiring board provided thereon a photoconductive layer in which its chargeability is changed by light exposure, and comprising an electrostatic image forming step containing at least image pattern exposure by UV light and a charging step subsequent thereto, a resist forming step by toner development, an alkali dissolution step of the photoconductive layer, and an etching step of a metal conductive layer.
2. Prior Art
In a conventional preparation of a printed wiring board, a printed circuit has generally been prepared onto an insulating substrate by the following steps. That is, laminating a photosensitive film onto a copper-clad laminated board wherein an insulating substrate is coated with a copper film, superposing a negative thereon, followed by exposure, development, removal of unnecessary portion of the copper film other than a circuit pattern, and finally, exfoliating the photosensitive layer. However, in this method using a photosensitive layer, since a thickness of the photosensitive film is generally as thick as about 50 xcexcm, a circuit pattern formed by exposure and development is not sharp, and it is difficult to laminate the photosensitive film uniformly on a copper film surface.
In order to improve resolution, etc. of the photosensitive film, there is disclosed a method of forming a photosensitive resist on a substrate by electrode position as is disclosed in Japanese Provisional Patent Publications No. 262855/1987, No. 4672/1989, etc. However, a photo resist for electrode position has generally a problem of low sensitivity. Particularly, it is difficult to irradiate inside the through holes, and in case of positive method where irradiated portion becomes soluble for a dissolving solution, it requires energy around several hundreds mJ/cm2 in order to give sufficient solubility. Therefore, it has been improper to use laser and the like for irradiation.
Further, as a preparation method for a printed wiring board other than that utilizing the photosensitive resist, there is disclosed a method of utilizing an electrophotographic method in West German Patents No. 2526720 and No. 3210577, Japanese Provisional Patent Publications No. 2437/1977, No. 48736/1982 and No. 168462/1984. In Japanese Provisional Patent Publication No. 129689/1988, there is disclosed a preparation method for a printed wiring board utilizing an electrophotographic material having specific sensitivity for wavelength of lasers. An example of using the electrophotographic method by directly drawing an image to be formed by laser on a substrate has already been applied for an electrophotographic material used in electrophotographic lithographic printing plate, etc. and a method has been now in a practical use that utilizes a laser scanning exposure, based on data directly sent from a computer without using a photomask, to form a high density image.
In a printed wiring board prepared by utilizing the electrophotographic method (hereinafter referred to as xe2x80x9celectrophotographic printed wiring boardxe2x80x9d), different from a photosensitive dry film resist or a liquid photo resist, it is possible to set a thickness of a resist small, thereby it is advantageous in coating and drying conditions, alkali developing condition, in keeping the etching factor of circuit patterns large enough after etching, so that it is excellent in reproducibility of fine lines and productivity. In addition, since it is a liquid resist, it is possible for a resist film to comply with unevenness of a substrate, thereby decreasing defects such as open circuit or leaching, etc. Further, there has been an increasing expectation for a practical use, since it is excellent in many properties such as maintenance of alkali developing solution, handling of a substrate after coating, ability for perfect protection of through holes, etc. as compared with other resist materials.
Preparation of the electrophotographic printed wiring board is carried out as follows. On the surface of a photoconductive layer of a wiring board in which a photoconductive layer was coated on a conductive support comprising an insulating substrate and provided thereon, a metal conductive layer, charging and exposure according to a wiring pattern are carried out to form an electrostatic latent image corresponding to an exposed portion. To this electrostatic latent image, toner developing treatment is carried out to obtain a toner image, and using this toner image as a resist, a portion of the photoconductive layer other than the toner image is removed by dissolution to prepare a resist image comprising the toner image and the photoconductive layer. Removal of unnecessary portion of the metal conductive layer by dissolution and succeeding processes for preparation of the printed wiring board can be carried out in the same manner as conventional methods.
In a method of preparing an electrophotographic printed wiring board wherein a wiring pattern is formed on both surfaces of the insulating substrate, as disclosed in Japanese Provisional Patent Publication No. 209606/1998, at least a metal conductive layer and a photoconductive layer are provided in this order on both surfaces of an insulating substrate, the obtained board is mounted on a flat table of an exposing device, adjusted to a proper place (positioning), then charging is conducted. Then, exposure is carried out on one surface of a photoconductive layer to form an electrostatic latent image. After turning over the board, positioning and charging are conducted again, followed by exposure on the other surface of the photoconductive layer to form an electrostatic latent image. After that, toner developing treatment and succeeding processes are conducted in the same manner as the above, to prepare a printed wiring board with circuit patterns formed on both surfaces.
However, according to this method, there is a problem that when the board on the flat table is turned over after exposure, the surface having the electrostatic latent image initially formed by exposure and charging makes a mechanically strong contact with the flat table of the exposing device, and electric charge distribution of the contacted surface is disturbed. Similarly, even after the electrostatic latent images are formed on the both surfaces, there is a problem such that the electrostatic latent image is distorted by contacting with a conveying member for transport to the toner developing process. Since an image quality of the toner image is largely dependent on the electric charge distribution of the electrostatic latent image, distortion of the electrostatic latent image produced is reflected on the toner image as it is, resulting a problem of shortcircuiting, breakage or open circuit, etc.
In addition, this direct circuit drawing method by laser using electrophotographic method requires an exposure dose as low as 1 to 50 xcexcJ/cm2, it is possible to use as laser a semiconductor laser which is less expensive and requires less power output. However, since its photoconductive layer has high photosensitivity for wavelength of 500 to 900 nm, there are problems that red laser diode sensor used for positioning of the printed wiring board during an image forming process causes an image fog at the photoconductive layer and that it is impossible to carry out the succeeding processes under visible light where the process are done efficiently from charging of the photoconductive layer, image-exposing, and until toner developing of the electrostatic latent image.
Further, a charge transfer material generally used for an organic electrophotographic material inherently has a function to transport a photo-carrier (a hole or an electron) generated from a charge generating material that has absorbed a visible light or infrared rays according to an electric field applied on the photoconductive layer. Generally, the charge generating material is a colored dye or pigment, while the charge transfer material is a compound that absorbs ultra violet rays and does not absorb infrared rays or a visible light. When it is considered to generate a photo-carrier by irradiating UV light that is absorbed by the charge transfer material, poly(vinylcarbazole) has been well known as a substance effectively generating a photo-carrier. However, it is not suitable to use it as a photosensitive resin in order to form an extra-fine pattern as seen in a printed wiring board, since it is extremely poor in a film-forming property, and also it is extremely immiscible with other resins with a good film-forming property. On the other hand, as a charge transfer material used for an organic electrophotographic material, there have recently been known compounds with low molecular weights including a hydrazone compound, a triphenyl amine compound, a stilbene compound, etc. However, those compounds have by themselves extremely low efficiency in generating photo-carrier. Therefore, in an electrophotographic material comprising a photoconductive layer constituted solely by the charge transfer material with a low molecular weight and a binder resin, and not containing a charge generating material, it has not yet been known a system having a practical photosensitivity for UV lights.
An object of the present invention is to provide a printed wiring board, by using an electrophotographic material having photosensitivity for a range of wavelength shorter than 500 nm, that is free from image defect even though it makes contact with a conveying member or a flat table of an exposing device during a pattern image forming process, that will not cause an image distortion by a sensor, and that enable to carry out the pattern image forming processes under visible light where the process is done efficiently.
The present inventors have made extensive and intensive studies for solving the above problems, and as a result, they have found that it is possible to exclude a mechanical contact from the processes after formation of the electrostatic latent image until prior to the toner developing, by initially exposing a wiring board having a photoconductive layer which changes its chargeability by light exposure on the surfaces of a conductive support which comprises an insulating substrate and metal conductive layers provided on the surface thereof through a resist pattern; and then, charging the photoconductive layer to form an electrostatic latent image; forming a toner image on the photoconductive layer by toner developing treatment; removing a portion of the photoconductive layer to which no toner is attached by dissolution to form a resist image; and removing a portion of the metal conductive layer other than a portion where the resist image is formed by etching. They have found that this process enables to prepare a printed wiring board with fewer defects such as residual copper, shortcircuiting, leaching or open circuit, etc.
The present inventors have also found that copper circuits can be formed on both surfaces of the wiring board by a process wherein the wiring board having photoconductive layers in which their chargeabilities are changed by light exposure provided on both surface of a conductive support which comprises an insulating substrate and metal conductive layers provided on both surface thereof is exposed through a resist pattern on one surface followed by the other, then, the both surfaces of the photoconductive layers are charged to form electrostatic latent images on both surfaces, followed by carrying out toner image formation, resist image formation, and etching of the metal conductive layers for both surfaces, either separately or simultaneously.
Further, the present inventors have found that by using a photoconductive layer comprising a charge transfer material with a low molecular weight having a specific chemical structure, and consisting no generally used colored charge generating material (an organic pigment, a sensitizing dye), it is possible to provide a wiring board that is able to form an image by exposing to UV light. It is possible to form an electrophotographic pattern image under visible light or yellow safe light by making this photoconductive layer not change its chargeability by light exposure with a wavelength of 500 nm or longer.
The present invention relates to a process for producing a printed wiring board which comprises the steps of:
a) exposing a wiring board having at least one photoconductive layer in which its chargeability is changed by light exposure on at least one surface of a conductive support which comprises an insulating substrate and at least one metal conductive layer provided at least one surface thereof through a resist pattern;
b) charging the photoconductive layer to form an electrostatic latent image;
c) forming a toner image on the photoconductive layer by toner developing treatment;
d) removing a portion of the photoconductive layer to which no toner is attached by dissolution to form a resist image; and
e) removing a portion of the metal conductive layer other than a portion where the resist image is formed by etching.
In the following, the embodiments of the present invention are explained in detail.
The photoconductive layer to be used in the present invention comprises an anthraquinone type dye represented by the formula (I), a charge transfer material, and a resin that is soluble for an alkali solution. 
In the formula (I), each of R1 and R2 represents an alkyl group, an aryl group, or an aralkyl group and those substituents may have a further substituent(s). R1 and R2 may be the same or different from each other.
As a charge transfer material to be used in the present invention, compounds represented by the formulae (II), (III), (IV), (V) and (VI) are preferred. 
In the formula (II), R3 represents a hydrogen atom, an alkyl group, or an aryl group, and Ar1 and Ar2 both represent an aryl group. Z represents an alkylene group with a carbon number of 3 or 4, that forms a 5-membered ring or 6-membered ring bonded to a pyrrolidine ring. Those substituents other than the hydrogen atom may be further substituted, and Ar1 and Ar2 may be the same or different from each other. 
In the formula (III), R4 represents a hydrogen atom, an alkyl group, or an aryl group, and Ar3 and Ar4 both represent an aryl group. Each of R5 and R6 represents a hydrogen atom or an alkyl group wherein at least one of R5 and R6 is an alkyl group. Y is an alkylene group with a carbon number of 1 or 2 that forms a 5-membered ring or 6-membered ring with two carbon atoms bonded to a pyrrolidine ring. Those substituents other than the hydrogen atom may be further substituted. Ar3 and Ar4, or R5 and R6 may be the same or different from each other. 
In the formula (IV), each of R7, R8 and R9 represents a hydrogen atom or an alkyl group, and each of R10 and R11 represents an alkyl group or an aryl group. Those substituents other than the hydrogen atom may be further substituted. R7, R8 and R9, or R10 and R11 may be the same or different from each other. 
In the formula (V), each of Ar5 and Ar6 represents an aryl group, and each of R12, R13, R14 and R15 represents an alkyl group or an aralkyl group. Those substituents may be further substituted. Ar5 and Ar6 or R12, R13, R14 and R15 may be the same or different from each other. 
In the formula (VI), each of Ar7, Ar8, Ar9 and R16 represents an aryl group, and those substituents may be further substituted. Ar7, Ar8, Ar9 and R16 may be the same or different from each other. n represents an integer of 1 or 2.
The photoconductive layer of the present invention may contain in addition to at least one of the charge transfer materials represented by the formulae (II), (III), (IV), (V) and (VI) and a binder resin, at least one of the compounds represented by the formulae (VII), (VIII), (IX), (X), (XI), (XII) and (XIII) in an amount of 0.1 to 30% by mass (% by mass is the same meaning as % by weight, hereinafter the same) based on the total amount of the charge transfer materials represented by the formulae (II), (III), (IV), (V) and (VI). 
In the formula (VII), each of R17, R18, R19 and R20 represents an alkyl group or an alkoxy group, which may be further substituted. R17, R18, R19 and R20 may be the same or different from each other. 
In the formula (VIII), R21 is a substituent on a naphthalene ring, representing a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, an alkylamino group, an alkoxy group, an alkenyloxy group, an aralkyloxy group or an alkenyl group. Q represents an aromatic hydrocarbon residue that is condensed to form a bond with an imidazoline ring. 
In the formula (IX), R22 is a substituent on a naphthalene ring, representing a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, an alkylamino group, an alkoxy group, an alkenyloxy group, an aralkyloxy group or an alkenyl group. R23 represents an alkyl group or an aryl group and may be further substituted. 
In the formula (X), R24 is a substituent on a benzene ring, representing a hydrogen atom, a halogen atom, or a nitro group. P represents an aromatic hydrocarbon residue that is condensed to form a bond with an imidazoline ring. 
In the formula (XII), each of Ar10 and Ar11 represents an aryl group and may be further substituted. Ar10 and Ar11 may be the same or different from each other. m represents an integer of 0 or 1. 
In the formula (XIII), Ar12 represents an aryl group and each of R25 and R26 represents an alkyl group which may be further substituted. R25 and R26 may be the same or different from each other. 1 represents an integer of 0 or 1.
Hereinbelow, specific examples of the anthraquinone type dye represented by the formulae (I) is listed below, however, the photoconductive layers are not limited to those examples. 
By adding a dye represented by the formula (I) to the photoconductive layer, the photoconductive layer is colored, and aspect of a resist pattern on a conductive layer of a printed wiring board before etching becomes dramatically visible as compared to one without addition of the dye.
As a dye for improving visual contrast of a resin layer, there have been known various kinds of dyes such as a triphenylmethane type dye, an azo type dye, a phthalocyanine type dye, a cyanine type dye, etc. In case of dyeing a photoconductive layer that uses an electrophotographic method, kinds of applicable dyes are extremely limited in practice from the reasons below. That is, since a triphenylmethane type dye and a cyanine type dye are cationic dyes, when they are contained in a photoconductive layer, an ionic conductivity of the photoconductive layer becomes large, thereby making it difficult to form an electrostatic latent image. On the other hand, an azo type dye with an excellent solubility for a solvent generally shows the maximum absorption wavelength for a visible light shorter than 550 nm, therefore, there has not been found a substance which satisfies an object to make the resist more recognizable, and is less expensive. In addition, a phthalocyanine type dye is less soluble for a solvent, therefore, it is difficult to add those dyes uniformly into the photoconductive layer. Moreover, it has a photoconductivity so that it is difficult to form an electrostatic latent image under visible light.
On the contrary, it was figured out that among the anthraquinone type dyes, one with a specific chemical structure represented by the formula (I) has a high solubility for a solvent, and it does not impair the electrophotographic property of the photoconductive layer. Since the dye represented by the formula (I) has no photoconductivity, spectral sensitization is not caused by generation of photo-carrier from the dye itself, or by addition of the dye. Therefore, it is possible to form an electrostatic latent image and carry out toner development under visible light or yellow safe light.
Further, it was found that by adding the dye represented by the formula (I) in a coating solution for forming a photoconductive layer of the present invention on a metal conductive layer, it is possible to prevent a deterioration of the coating solution during preservation under heating over a period of time. Although it is not clear what kind of chemical change in a coating solution occurs during preservation under heating over a period of time, it is a matter of importance to succeed in dramatically improving stability of the coating solution by having a dye with a specific chemical structure co-existed with a mixed coating solution system comprising a charge transfer material and an alkali-soluble resin, in terms of establishing a practical process for preparing a wiring board.
An amount of the dye represented by the formula (I) to be added to the photoconductive layer may be optionally set in a range not to significantly lower a concentration of the charge transfer material in the photoconductive layer. It is preferably from 0.1% to 10% by mass based on the total amount of a solid portion in the photoconductive layer.
Next, specific examples of compounds represented by the formula (II) to be used for the photoconductive layer of the present invention are shown below, however, the present invention is not limited to those examples. 
Next, specific examples of compounds represented by the formula (III) to be used for the photoconductive layer of the present invention are shown below, however, it is not limited to those examples. 
Next, a specific example of compounds represented by the formula (IV) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, specific examples of compounds represented by the formula (V) to be used for the photoconductive layer of the present invention are shown below, however, it is not limited to those examples. 
Next, a specific example of compound represented by the formula (VI) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, a specific example of compound represented by the formula (VII) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, specific examples of compounds represented by the formula (VIII) to be used for the photoconductive layer of the present invention are shown below, however, it is not limited to those examples. 
Next, a specific example of compound represented by the formula (IX) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, a specific example of compound represented by the formula (X) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, a specific example of compound represented by the formula (XII) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
Next, a specific example of compound represented by the formula (XIII) to be used for the photoconductive layer of the present invention is shown below, however, it is not limited to this example. 
By adding compounds represented by the formulae (VII) to (XIII) in an amount of 0.1 to 30% by mass based on the total amount of the charge transfer materials represented by the formulae (II) to (VI), it is possible to further reduce a residual charge at an exposed portion as compared to a sample without being added compounds represented by the formulae (VII) to (XIII). The compounds represented by the formulae (VII) to (XIII) do not have spectrally sensitizing property, and therefore, it is possible to carry out formation of the electrostatic latent image and toner development under visible light or yellow safe light in a system where the compound of the formulae (VII) to (XIII) are added.
The action and mechanism for the effect caused by the compounds represented by the formulae (VII) to (XIII) are not clear in detail, however, it is assumed as follows. By exposing a photoconductive layer with UV light, the charge transfer materials of the formulae (II) to (VI) absorb the UV light and generate a large amount of electrons. As a result, the change in chargeability of the photoconductive layer is generated in the exposed portion of the photoconductive layer, and by charging followed by exposure, an unexposed portion is normally charged, while the exposed portion is selectively uncharged, thereby an electrostatic latent image is formed. Since the charge transfer materials of the formulae (II) to (VI) are excellent in positive charge transfer, but inferior in electron transfer, the difference in chargeability is easily lost by re-binding of the generated electrons and positive charges. The compounds of the formulae (VII) to (XIII) have a property of an electron acceptor, and they can temporarily accept the charges generated from the compounds of the formulae (II) to (VI) by irradiation of the UV light. Also, they are excellent in ability to transfer the electrons once accepted. Therefore, when charging is carried out after the UV light exposure, the electrons once accepted by the compounds of the formulae (VII) to (XIII) are released again by application of the electrical field, and the charges are favorably lost on the surface of the exposed portion by the UV light.
As a laminated board obtained by providing a metal conductive layer on an insulating substrate in accordance with the present invention, a typical one is that comprising paper-substrate phenol resin or a glass-substrate epoxy resin laminated by a copper film, etc. as a metal conductive layer. Examples of those laminated board are described in xe2x80x9cPrinted Circuit Technical Manualxe2x80x9d (edited by Nippon Printed Circuit Industry Association, published by Nikkan Kogyo Shinbun-sha in 1987), and desired laminated board can be used.
A thickness of the insulating substrate is generally from about 80 xcexcm to about 3.2 mm, and the material and the thickness thereof are chosen according to the finally used embodiment as a printed wiring board. In case of using a thin substrate, it may be used by laminating several of them.
The metal conductive layer provided on the insulating substrate of the laminated board can be chosen from those having various thickness and those with a thickness of 5 to 35 xcexcm is generally used. However, those having a thickness thinner or thicker than the above range may be used. As wiring density becomes higher and the width between the wiring becomes finer, it is more preferable to use a thinner metal conductive layer. As a metal used for the metal conductive layer, there may be mentioned copper, silver, aluminum, stainless, nichrome, tungsten, etc.
As specific examples of an alkali-soluble resin to be used in the photoconductive layer of the present invention, there may be mentioned styrene/maleic acid monoester copolymer, methacrylic acid/methacrylic acid ester copolymer, styrene/methacrylic acid/methacrylic acid ester copolymer, acrylic acid/methacrylic acid ester copolymer, styrene/acrylic acid/methacrylic acid ester copolymer, methacrylic acid/methacrylic acid ester/acrylic acid ester copolymer, acrylic acid/acrylic acid ester/methacrylic acid ester copolymer, vinyl acetate/crotonic acid copolymer, vinyl acetate/crotonic acid/methacrylic acid ester copolymer, styrene/vinyl benzoate copolymer or a phenol resin such as polyvinyl phenol resin, novolak resin, etc. As the resin to be used in the present invention, any resin can be used as long as it has a good film-forming property, is soluble for an aqueous alkali solution, and has a resistance against an etching solution to be used in removing the metal conductive layer, and it is not limited to the above-mentioned resins.
A mixing ratio of the charge transfer materials of the formulae (II) to (VI) to be used in the photoconductive layer of the present invention based on the binder resin is preferably about 0.1 to 100% by mass and particularly preferably 5 to 40% by mass.
Preparation of the photoconductive layer of the present invention is carried out by dip coating, bar-coating, spray-coating, roll-coating, spin-coating, electrodeposition, etc. A coating solution is prepared by dissolving components constituting the photoconductive layer in a proper solvent. Further, plasticizer, surfactant, and other additives can be added to the coating solution in addition to the charge transfer materials and the resin, for the purpose of improving physical properties of the film and viscosity of the coating solution.
As a solvent to be used for preparation of the coating solution, anything may be used as long as it can dissolve the charge transfer materials and the binder resins uniformly. Specifically, there may be mentioned alcohols such as methanol, ethanol, 1-propanol, 1-methoxy-2-propanol, etc.; ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxy ethane, ethylene glycol monomethyl ether, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, etc.; aromatic hydrocarbons such as toluene, xylene, etc.; esters such as ethyl acetate, methyl acetate, isobutyl acetate, etc.; amides such as N,N-di-methylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.; and dimethyl sulfoxide, etc., however, it is not limited to these, and it may be properly chosen according to a coating method and drying condition, etc. A concentration of the solid portion of the coating solution may also be properly chosen according to a coating method and drying condition, etc. Regarding a thickness of the photoconductive layer of the present invention, when it is too thick, problem arises that potential difference of an electrostatic latent image between the exposed portion and the unexposed portion is hard to be generated, and this promotes a deterioration of an dissolving solution in a process where the photoconductive layer is dissolved by alkali. On the other hand, if the photoconductive layer is too thin, it is impossible to give enough electric charge in a step of charging of the photoconductive layer required for toner developing of the electrophotography. Preferred thickness of the photoconductive layer is 0.5 to 20 xcexcm, and more preferably, 1 to 10 xcexcm.
As a method for exposing the photosensitive material, there may be mentioned reflective image exposure, contact exposure through a transparent positive film, direct projection exposure, using UV fluorescent light, xenon lamp, high-pressure mercury vapor lamp, etc. as a light source, and scanning exposure using UV laser light. In case of using the scanning exposure, it can be carried out by changing a wavelength of laser light sources such as Hexe2x80x94Ne laser, Hexe2x80x94Cd laser, Argon laser, Krypton ion laser, ruby laser, YAG laser, nitrogen laser, dye laser, excimer laser, etc. with the second harmonic generation device to an appropriate wavelength according to light emitting wave length, or it can be carried out by using liquid crystal shutter and micro mirror array shutter.
After completing the image exposure, charging is carried out and a static latent image is formed. As a method for charging, there have been known a conventional non-contact charging such as corotron method and scorotron method, etc., and a contact charging method such as conductive roll-charging method, etc. Any method can be used as long as the photoconductive layer of the present invention in which its chargeability is changed by exposure can be charged uniformly.
An electrostatic latent image formed by statically charging process is developed by toner developing, and a toner image is formed. As a method for forming a toner image by electrophotographic method, there may be used a drying development (cascade development, magnetic brush development and powder crowd development) and a liquid development using a liquid toner in which toner particles are dispersed in a proper insulating solution. Among them, liquid development is more preferable for the present invention since toner particles are stable and have smaller particle diameters, thereby making it possible to form a finer toner image.
As a toner to be used in the present invention, there may be used a wet type toner used for an electrophotographic printing board, and it should show resistance against a removing of non-wiring portion of the photoconductive layer by dissolution in the following step. In view of this, as a component of the toner particle there is preferably contained, for example, an acrylic resin comprising an acrylate, a methacrylate, etc.; a vinyl acetate resin; copolymer of vinyl acetate and ethylene or vinyl chloride, etc.; a vinyl chloride resin; a vinylidene chloride resin; a vinyl acetal resin such as poly(vinyl butyral); polystyrene; copolymer of styrene and butadiene or a methacrylate, etc.; polyethylene, polypropylene and chlorides thereof; a polyester resin such as polyethylene terephthalate, polyethylene isophthalate, etc.; a polyamide resin such as polycapramide, polyhexamethylene adipamide, etc.; vinyl-modified alkyd resin; gelatin; a cellulose ester derivative such as carboxymethyl cellulose, etc.; and wax. Also, a dye or a charge controller may be added to the toner in the range which does not cause an unfavorable effect on development or fixing, etc. Moreover, the charge of the toner should be selected to be positive or negative based on statically charging polarity of the photoconductive layer upon corona charging.
As a method for development, there may be employed either reverse development method in which an exposed portion is developed while applying appropriate bias voltage, using toner having the same polarity as those of the electrostatic latent image, or normal development in which an unexposed portion is developed using toner particles having different polarity from those of the electrostatic latent image. The formed toner image can be fixed by, for example, heating fixation, pressure fixation, solvent fixation, etc. Using the thus formed toner image as a resist, the photoconductive layer is removed by dissolving solution to obtain a resist image of wiring which comprises a laminated board and provided thereon a photoconductive layer and the toner image.
As means for removing a portion of the photoconductive layer other than a toner image, a processor for a printing plate of non-image portion dissolving type may be basically employed using a dissolving solution. The dissolving solution to be used in the present invention contains a basic compound. For examples of the basic compound, there may be mentioned an inorganic basic compound such as an alkali silicate, an alkali hydroxide, an alkali phosphate, an alkali carbonate, ammonium phosphate, ammonium carbonate, etc., and an organic basic compound such as ethanolamines ethylenediamine, propanediamines, triethylenetetramine, morpholine, etc. The above-mentioned basic compounds may be used solely or as a mixture thereof. For a solvent of the dissolving solution, water is preferably used.
An exposed portion of the metal conductive layer other than the resist image of wiring is removed by etching. In an etching process, a method described in xe2x80x9cPrinted Circuit Technical Manualxe2x80x9d (edited by Nippon Printed Circuit Industry Association, published by Nikkan Kogyo Shinbun-sha in 1987) maybe used. Any etching solution may be used so long as it can remove the metal conductive layer by dissolution and at least the photoconductive layer has a resistance against it. Generally, if a copper layer is employed for the metal conductive layer, an aqueous solution of ferric chloride, cupric chloride, etc. may be used.
As in the case of preparing a printed wiring board utilizing a general resist such as resist ink, liquid resist, dry film photo-resist, etc., a resist image of wiring portion can be removed after etching process, by treating with further more alkaline solution than that used in removal of the non-wiring portion. It is possible to use an organic solvent which dissolves a binder resin of the photosensitive layer, such as methyl ethyl ketone, dioxane, methanol, ethanol, propanol, etc.